1. Field of Invention
The present invention relates to fiber optic bundles and, more particularly, is directed towards a fiber optic bundle beam expander.
2. Description of the Prior Art
Generally, image intensifier tubes are provided with straight fiber optic bundle output sections. Generally, in viewing systems having such an image intensifier tube, a lens magnifier is used to view the image at output face of the straight fiber optic bundle. If the numerical aperture of the fiber optic output face is substantially unity, as in the case of straight fibers, and if the magnifier is made to accept a high numerical aperture, the viewing system can provide high magnification with two-eyed viewing. The requisite condition is that the fiber optic output numerical aperture be sufficient to fill the high numerical aperture of the lens which provides an exit pupil large enough to be seen with both eyes. The output numerical aperture of a twisted fiber bundle or of a tapered fiber magnifier is limited, by the nature of total internal reflection, to somewhat less than unity and is insufficient to fill the lens numerical aperture as hereinbefore noted. A random diffuser on the output of a fiber optic bundle spreads the energy through a large solid angle, portions of which can not be used by the eyes. A need has arisen for a fiber optic bundle expander for tapered and twisted fiber optic bundles which does not suffer from the heretofore mentioned disadvantages.